Pressure-sensitive adhesive tapes are used for a variety of holding, protecting, sealing, masking and covering purposes. Pressure-sensitive adhesive tapes comprise a substrate and an adhesive. Pressure-sensitive adhesives generally comprise polymeric materials which adhere with a limited amount of applied force such as finger pressure and are permanently tacky.
In the medical area pressure-sensitive adhesive tapes are used for many purposes and are particularly popular for securing first aid dressings. For this use it is most desirable if the tape is compliant, adherent and non-irritating to the skin without causing damage on removal.
In order to attain the above-mentioned objectives, the pressure-sensitive adhesives useful for first aid dressings require a delicate balance of properties. It is necessary to control the viscosity and elasticity of the adhesives to provide an adhesive which initially adheres well to the skin and maintains adhesion for a selected interval without leaving a residue when removed from the skin. Further, the adhesive desirably remains non-irritating to the skin during the interval, and is compatible with various tape backings.
It is known to blend polymers to obtain various properties, however, it is difficult to obtain such blends which provide most or all of the above-mentioned desired properties. Furthermore, blends, i.e. initially homogeneous mixtures of polymers dispersed in solvents, may have a tendency to separate into non-homogeneous mixtures. This separation process is generally undesirable since it provides a mixture which lacks the desirable properties of homogeneous mixtures. It is particularly difficult to blend polymers with dissimilar properties, e.g. blending hydrophobic polymers with hydrophilic polymers is exceedingly difficult. Hydrophobic materials are by their very nature not readily mixed with hydrophilic materials. It is difficult to obtain stable blends of dissimilar polymers which do not separate even when blended in a compatible solvent. It is even more difficult to obtain a blend of dissimilar polymers which provides the desirable properties of both of the polymeric components.
Medical tapes which adhere well to moist skin over extended periods of time generally require adhesives which are substantially hydrophilic and polar in character. One such class of adhesives is described in PCT Application WO 84/03837 of Snyder and Spence (hereinafter "Snyder") entitled "Adhesive and Adhesive-Coated Sheet Material for Moist Skin" which is hereby entirely incorporated by reference. The adhesives of Snyder comprise a copolymer of copolymerized A, B and C monomers wherein A is a hydrophobic monomeric acrylic acid ester of a non-tertiary alcohol, said alcohol having from 4 to 14 carbon atoms; B is a hydrophilic monomer which has a vinyl group copolymerizable with the A monomer and is other than acrylic acid, itaconic acid, acrylamide, methacrylamide, lower alkyl-substituted acrylamide, and N-vinyl-2-pyrrolidone, the amount by weight of B monomer being about 5 to 30% of the total weight of all monomers in the copolymer; and C is at least one polar monomer copolymerizable with the A and B monomers, selected from the group consisting of acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylamide, lower alkyl-substituted acrylamide, and N-vinyl-2-pyrrolidone, the amount by weight of C monomer being about 0.5 to 30% of the total weight of all monomers in the copolymer; wherein the A, B and C monomers are copolymerized to form a polymeric backbone and the combination of A, B and C monomers being such as to provide an adhesive-coated sheet material with an initial dry skin adhesion value of at least about 0.75 Newton per 100 millimeters of width, a dry skin adhesion value after 48 hours of not more than about 12 Newtons per 100 millimeters of width, and a moist skin adhesion value of at least about 2.2 Newtons per 100 millimeters of width. Although these adhesives include one somewhat hydrophobic comonomer, the resultant adhesives are hydrophilic.
The preferred B monomer disclosed in Snyder is a hydrophilic macromolecular monomer, and the preferred hydrophilic macromolecular monomer has the general formula X-Y-Z, wherein
X is a vinyl group copolymerizable with the A monomer,
Y is a divalent linking group; and
Z is a monovalent polymeric moiety comprising a polyether essentially unreactive under copolymerizing conditions.
The pressure-sensitive adhesives and pressure-sensitive adhesive-coated sheet materials of the Snyder invention exhibit a balance of properties which render them particularly useful in medical and surgical applications involving adhesion to skin. These adhesives and adhesive-coated sheet materials adhere suitably to moist skin. These adhesives and adhesive-coated sheet materials further possess all of the other attributes required of a suitable adhesive or adhesive-coated sheet material for use in applications involving adhesion to normal skin. Specifically, these adhesives and adhesive-coated sheet materials exhibit suitable initial adhesion to dry skin and are removed from the skin without injury thereto or undesirable irritation thereof.
Another class of adhesives which are used as skin adhesives for medical applications are described in U.S. Pat. No. 4,693,776 of Krampe, Moore and Taylor (Krampe) entitled "Macromer Reinforced Pressure Sensitive Skin Adhesive" which is hereby entirely incorporated by reference. The adhesives of Krampe comprise a copolymer of copolymerized A, B, and C monomers wherein A is a monomeric acrylate or methacrylate ester of a non-tertiary alcohol, said alcohol having from 1 to 14 carbon atoms with the average number of carbon atoms being about 4-12; B, when used, is at least one ethylenically-unsaturated compound copolymerizable with said monomeric acrylate ester, the amount by weight of B monomer being up to 25% of the total weight of all monomers; and C is a macromer having the general formula: X-(Y).sub.n -Z wherein X is a vinyl group copolymerizable with said A and B monomers; Y is a divalent linking group; where .sub.n can be zero or 1; and Z is a monovalent polymeric moiety having a T.sub.g greater than about 20.degree. C. and a molecular weight in the range of about 2,000 to about 30,000 and being essentially unreactive under copolymerization conditions; wherein said vinyl group and said A and B monomers form a polymeric backbone having pendant therefrom said polymeric moieties (Z) and wherein the weight of said C macromer and the inherent viscosity of the copolymer are such that the adhesive composition has a creep compliance value of at least about 1.2.times.10-.sup.5 cm.sup.2 /dyne.
The skin adhesive coated sheet is preferably in the form of a tape or dressing which can be applied to skin to yield an enhanced level of initial adhesion to the skin without objectionable increase in adhesion over time.
These adhesives exhibit desirable high initial adhesion to skin, in part because of the hydrophobic nature of the macromer comonomer.
Thus, the hydrophilic adhesives of Snyder and the more hydrophobic adhesives of Krampe each provide highly desirable properties for a first aid dressing. One skilled in the art would not expect that mixtures of these adhesives would provide stable blends which would exhibit the desirable properties of both of the polymeric components. Indeed, one skilled in the art would expect that mixtures of solutions of these polymers would tend to separate into non-homogeneous mixtures of polymers.